In many instances the treatment of separate production intervals (zones) in a well has been accomplished by casing the well and thereafter perforating a zone to be treated for fracturing, gravel packing or the like. This requires that the well be cased in the zone to be treated and that perforations be placed in the casing to permit access to the subterranean production formation. This can require multiple trips of tubing into the well for operations, to exchange tooling, or the like. Further this can, in some instances, lead to multiple cemented pipe sizes being required to isolate the wellbore from the uppermost to the deepest production interval. Further when cemented pipe is used, it is not always possible to achieve good initial and long term cement isolation between production intervals. Also the area of perforations contributing production to the wellbore are small relative to the inside diameter of the well and can limit the flow rate from the treated formation.
The geometry of the fracture that can be placed within a cased hole wellbore can also be limited by the casing ID that can be installed across the production intervals and erosion of small flow areas in fracture placement tools and erosion of the casing.
Multiple intervals have been treated in a cased hole with fracture treatments without the use of screens. However, these operations require either wellbore cleanout to remove the treating fluid, including gravel or proppant from the wellbore after the treatment or each fracture treatment to be over-displaced to the formation.
These procedures result in substantial expense and pose certain problems with respect to optimum production of fluids from the formation.
Currently open-hole gravel packing operations are limited to treating single or multiple production intervals in a single treatment operation. In a very few instances, open hole fracture pack operations have been employed but were limited to treating a single production interval or multiple production intervals in a single treatment. This may not provide the optimum treatment or production for each production zone.
In some instances it has been possible to treat selected zones in open hole wellbores by the use of packers, or packers and valves, to isolate the zones for fracturing and the like. However, all such systems typically require the use of packers which are set to isolate the system to be treated or the like. Further it is generally necessary to remove the treating fluid, including gravel or proppant from the wellbore after the treatment is complete or to over-displace each fracture treatment to the formation and to close mechanical fracturing valves.
Since in many instances, a plurality of production intervals may be penetrated by a single open hole wellbore it would be highly desirable to be able to treat and produce these intervals independently in an uncased wellbore penetrating these intervals. Accordingly a considerable effort has been directed to developing such a method.